1. Field of the Invention
The present invention relates to a storage device, method, and program for controlling a tape speed to manage a tape drive buffer.
2. Description of the Related Art
When data is being written from a host, data is stored in the buffer memory (also called a buffer) of the tape storage device (tape drive). When the writing speed of the drive to the tape (drive transfer rate) is slower than the data reading speed of the host (host transfer rate), the buffer memory becomes full. When the buffer memory becomes full, the tape drive usually rewinds the tape medium in an operation called “backhitch”. Backhitch takes a few seconds (2 to 5 seconds). During the backhitch operation, the tape drive cannot write data to the tape medium or read data from the buffer. Thus, the backhitch operation adversely affects the overall data transfer rate because the host has to wait to read and write during the backhitch. When data is read by the host, the tape drive performs a backhitch when the buffer memory becomes empty.
FIGS. 1a and 1b show a tape speed changing method of the prior art. FIG. 1a shows a backhitch operation performed when the drive speed is changed. The tracking capability of the drive transfer rate is not sufficient with respect to the host transfer rate when the host transfer rate is significantly greater than the host transfer rate, or there are intermittent fluctuations in the host transfer rate. The host has to wait to write (2-5 seconds) during a backhitch. FIG. 1b shows intervals of written data on a tape being minimized before and after a tape speed change during writing performed before and after a backhitch operation.